Elongated energy-absorbing structures such as vehicle lower rails may be designed to absorb impact loads during front and rear-end collisions, for example. It is generally desirable to design such structures so as to maximize energy-absorption while minimizing the weight and bulk of the structure. However, existing designs may absorb energy in a manner which leads to undesirable bucking failure at an unpredictable location along the length of the rail. A design which fails in such a mode may be relatively inefficient and ineffective as an energy absorber.